I have an English sporting rifle of similar age, that has been in the family for generations, and is currently getting an appraisal for restoration in Ontario. The guy I chose is an expat Brit, trained in London, was admitted as a "Freeman Of The Worshipful Company Of Gunmakers Of The City Of London" in 1966. The guy that made my old rifle was admitted to the same group in 1801. I am still waiting for his appraisal, and have no actual experience with the guy, but I could PM you his address, if that helps...
Glen